The present methods of obtaining spark advance in ignition systems is to use a rotating charge/trigger assembly or a stationary charge/trigger assembly with a speed dependant trigger mechanism. The first method uses a stator plate containing charge and trigger coils and rotated in unison with the throttle control. This usually requires a bronze bearing for the stator plate and elaborate cams to obtain the desired spark advance. Contamination and use wear the bearing and stress the wires connecting the stator and the electronic ignition module. Any change in the advance characteristics requires a change in the cams with consequent tooling cost.
The speed dependent trigger used in the second method obtains the electronic advance from the changing slope of the trigger pulse and thus requires elaborate shaping of the magnetic structure. The result is inflexible, has an advance characteristic which is limited in range, and has undesirable engine performance at idle speed (due to the initial advance). The advance cannot be varied enough at high engine speed.